Method and apparatus for controlling etch processes during fabrication of semiconductor devices

ABSTRACT

A method for controlling etch processes during fabrication of semiconductor devices comprises tests and measurements performed on non-product and product substrates to define an N-parameter CD control graph that is used to calculate a process time for trimming a patterned mask to a pre-determined width. An apparatus for performing such a method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 10/238,453, filed Sep. 9, 2002, which claimsbenefit of U.S. provisional patent application Ser. No. 60/361,064,filed Mar. 1, 2002. This application claims benefit of U.S. provisionalpatent application Ser. No. 60/463,757, filed Apr. 18, 2003. Each of theaforementioned related patent applications is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to semiconductor substrateprocessing systems. More specifically, the present invention relates tocontrolling etch processes in a semiconductor substrate processingsystem.

2. Description of the Related Art

To increase operational speed, devices (e.g., transistors, capacitors,and the like) in integrated microelectronic circuits have become eversmaller. The minimal dimensions of features of such devices are commonlycalled in the art, critical dimensions, or CDs. The CDs generallyinclude the minimal widths of the features, such as lines, columns,openings, spaces between the lines, and the like.

One method of fabricating such features comprises forming a patternedmask (e.g., photoresist mask) on the material layer beneath such a mask(i.e., underlying layer) and then etching the material layer using thepatterned mask as an etch mask.

The patterned masks are conventionally fabricated using a lithographicprocess when a pattern of the feature to be formed is opticallytransferred into a layer of photoresist. Then, the photoresist isdeveloped, unexposed portions of the photoresist are removed, while theremaining photoresist forms a patterned mask.

An etch mask generally is, in a plan view, a replica of the feature tobe formed (i.e., etched) in the underlying layer. As such, the etch maskcomprises elements having same critical dimensions as the feature to beformed. Optical limitations of the lithographic process may not allowtransferring a dimensionally accurate image of a feature into thephotoresist layer when a CD of the element is smaller than opticalresolution of the lithographic process.

To overcome limitations of the lithographic process, the photoresistmask may be fabricated using a two-step process. During a first step,the lithographic process is used to form the mask having elements thatdimensions that are proportionally greater (i.e., scaled up) than thedimensions of the features to be formed. During a second step, suchscaled-up elements are trimmed (i.e., isotropically etched) to thepre-determined dimensions. The trimmed photoresist mask is then used asan etch mask during etching the underlying material layer or layers.

Dimensional accuracy of the etch features generally defined by thecorresponding elements of the trimmed photoresist mask. Manufacturingvariables of the trimming process result in a broad statisticaldistribution (i.e., a large σ, where is σ a standard deviation) of theCDs within a group (i.e., batch) of the wafers. When such trimmedphotoresist masks are used as the etch masks, critical dimensions of theetched features may be beyond an acceptable range for such dimensions,i.e., the features may be defective.

Therefore, there is a need in the art for an improved method andapparatus for controlling etch processes during fabrication ofsemiconductor devices in a semiconductor substrate processing system.

SUMMARY OF THE INVENTION

The present invention is a method for controlling etch processes duringfabrication of semiconductor devices in a semiconductor substrateprocessing system. The method comprises pre-determined tests andmeasurements that are performed on non-product and product substrates.In one embodiment, the method is used to define an N-parameter criticaldimension (CD) control graph that is used to calculate a process timefor trimming a patterned mask to a pre-determined width. An apparatusfor performing the inventive method comprises an etch reactor, aprocessor and a tool for measuring characteristics of the patterned maskand/or the etched feature.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a block diagram of an apparatus according to an embodiment ofthe present invention;

FIG. 2 is a process flow diagram for an embodiment of the presentinvention;

FIG. 3 is a flow chart illustrating sequential steps in a methodaccording to an embodiment of the present invention;

FIGS. 4A-4D are graphical representations of trim processcharacteristics for use with an embodiment of the present invention;

FIGS. 5A-5B are graphical representations of the results of processingwafers using an embodiment of the present invention;

FIGS. 6A-6E schematically illustrate processing modules according toembodiments of the present invention;

FIG. 7 is a flow chart illustrating sequential steps in a methodaccording to an embodiment of the present invention;

FIGS. 8A-8B depict flow diagrams of methods for generating anN-parameter critical dimension (CD) control graph and for runningproduction wafers with feed forward;

FIGS. 9A and 9B illustrate the function of a feed-forward controller;and

FIG. 10 is a graphical representation a 2-parameter critical dimension(CD) control graph used to calculate a duration of the trimming processin one embodiment of the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

A first embodiment of the present invention utilizes optical CD (OCD)metrology to inspect every wafer to determine pre-etch CD and profile,then uses the inspection results to determine process parameters, suchas resist trim time and/or etch parameters. In further embodiments ofthe invention, OCD metrology is used post-trim and/or post-etch toinspect wafers to determine the post-trim and/or post-etch CD andprofile. The invention then uses the post-trim and/or post-etchinformation to develop an N-parameter trim surface for controllingvarious parameter of the trim process and/or etch process onsubsequently processed wafers. In this way, the present inventionenables accurate final CD and profile dimensions. The present inventionaddresses the problem of CD control by reducing CD variation by feedingforward and backward information relating to photoresist mask CD andprofile to adjust (1) the next process the inspected wafer will undergo(e.g., the photoresist trim process); or (2) adjust processes for futurewafers. In certain embodiments of the present invention, pre-etch CD andprofile measurement, etching, cleaning, and post-etch CD measurement areperformed-entirely under controlled environmental conditions. Byproviding etching, cleaning and measurement tools on a mainframe and/orfactory interface, a wafer can be etched, cleaned and inspected beforebeing returned to a cassette, thereby reducing processing time and cost.

OCD metrology techniques as employed by the present invention areadvanced process control (APC) enablers and utilize novel technology tothe CD measurement world where the current SEM-based systems arebecoming inadequate. For example, normal incidence spectroscopic OCDmetrology systems provide detailed line profiles not possible within-line non-destructive SEMs. The compact size and speed of OCDtechnology enables the measurement system of the present invention to befully integrated into a process tool, such as Applied Materials' DPSIIetch system. When combined with APC software, this provides a complete,feed-forward solution for wafer-to-wafer closed loop control.

An example of a processing step that benefits from the completefeedforward solution of the present invention is etch processing that issensitive to incoming photoresist (PR) dimensions. CD control isparticularly critical for gate etch, in which the device speed isdetermined by the final gate CD. Here, the variation in incoming resistmask CD creates a proportional variation in the final etched CD.Measuring the incoming resist CD prior to etching enables the etchprocess to be tuned to compensate for the variations due to lithography.

According to the methodology of the present invention, an underlyinglayer, such as a conductive layer, is formed on a wafer, and a patternedlayer, such as a photoresist mask, is formed on the underlying layer, asby a photolithography process at a “photo cell” (e.g., exposure at astepper followed by photoresist development). A pattern on the mask isinspected using an integrated metrology unit, such as an opticalinspection tool, to determine its CD and profile. The wafer is thentransferred to a conventional etch chamber, where the measuredphotoresist CD and profile are used by the processor to adjust thephotoresist trim recipe (e.g., the trim time), also taking into accountthe implicit etch uniformity performance of the etcher and thenonlinearity of the trim curve.

The underlying layer is thereafter etched using the trimmed photoresistpattern as a mask. After etching, the wafer is optionally cleaned, as byan ash photoresist strip followed by a wet cleaning step, andtransferred back to the integrated metrology unit, where the CD, profileand depth of features formed by the etch process are measured andcompared to the desired dimensions. Such information can be fed back tothe processor (e.g., to compensate for etch process drift or photo cellproblems) by adjustment of the trim recipe when etching the next wafer.

By taking into account photoresist CD and profile variation whenchoosing a resist trim recipe, the present invention decouples post-etchCD from pre-etch CD and profile. By measuring the incoming resist CD andadjusting the trim time, the etch process can compensate for variationsin lithography on successive wafers. With automatic compensation ofincoming resist CD from the lithography step, a much tighterdistribution of post-etch CD is achieved by the present invention, andthe final CD uniformity becomes a realistic etch specification withoutimpacting the productivity of the etch tool.

To optimize production efficiency, post-etch measurements for closedloop control must be made directly on the wafer before it leaves theetcher. CDSEM measurement can require time-consuming wet cleaning,particularly when etch byproducts cling to the sidewalls of the etchedstructure. Such deposits render top-down CDSEM post-etch measurementsinaccurate. Optical CD (OCD) metrology is insensitive to thin layers ofdeposits, making it possible to take accurate in-situ post-etchmeasurements, eliminate the cycle time penalty of wet cleaning, andimmediately feed back data to the process controller. The accuracy ofthis technique was confirmed by comparing pre-clean and post-cleanpost-etch OCD measurements from nine locations on a hardmask polysilicongate wafer. Results showed an average difference of 0.06 nm and astandard deviation of 0.3 nm, well within the resolution of themeasurement tool.

An exemplary embodiment of the present invention is implemented using aninspection tool in a processing line 300, as shown in FIG. 1, comprisinga measuring tool 310, e.g., an optical inspection tool such as the NanoOCD 9000 available from Nanometrics of Milpitas, Calif., or an opticalimager as disclosed in U.S. Pat. No. 5,963,329. Optical measuring tool310 can utilize scatterometry or reflectometry techniques. The use ofscatterometry for inspection tools is disclosed in Raymond,“Angle-resolved scatterometry for semiconductor manufacturing”,Microlithography World, Winter 2000. The use of reflectometry forinspection is taught in Lee, “Analysis of Reflectometry and EllipsometryData from Patterned Structures”, Characterization and Metrology for ULSITechnology: 1998 International Conference, The American Institute ofPhysics 1998.

Processing line 300 further comprises a processor 320, which performsthe analysis disclosed herein electronically, and a monitor 330 fordisplaying results of the analyses of processor 320. Processor 320 canbe in communication with a memory device 340, such as a semiconductormemory, and a computer software-implemented database system 350 known asa “manufacturing execution system” (MES) conventionally used for storageof process information. Processor 320 can also be in communication withpreviously-described photo cell 360 and etcher 370.

An embodiment of the present invention will now be described in detailwith reference to FIGS. 1-3. Referring now to the process flow diagramof FIG. 2, a wafer W to be processed by an etcher comprises a substrate200 upon which is formed a conductive layer 210, such as polysiliconlayer by deposition processing. A patterned photoresist layer 250 (i.e.,a photoresist mask formed at photo cell 360) having patterns P is formedon conductive layer 210. An anti-reflective coating (ARC) layer (notshown) may be formed in a conventional manner between conductive layer210 and photoresist layer 250 to aid the photolithographic process.Alternatively, a silicon nitride layer (not shown) can be formed onconductive layer 210 that is to be patterned to form a “hard mask” byetching using photoresist layer 250. Patterns P have an initial CDreferred to as CD₀ in FIG. 2. As shown in the flow chart of FIG. 3,wafer W is brought from photo cell 360 to measuring tool 310 at step3000, where the CD and profile of pattern P are optically measured. TheCD and profile measurements are typically taken at several locations(i.e., patterns P) on wafer W. The number of measurements is ultimatelylimited by the etch process throughput requirements, and influenced bythe process' maturity and past performance. Generally, the less maturethe process, the greater the number of measurements should be taken.Typically, about five sample measurements are taken including, e.g.,top, left, bottom, right and center of the wafer. The CDs and profilesof the measured features can then be averaged before being employed insubsequent steps of the present methodology.

Measuring tool 310 can directly measure CD and profile of certainpatterns on photoresist layer 250, such as trenches and the like usingconventional optical inspection techniques. For example, a rigorouscoupled wave analysis (RCWA) can be performed, wherein a CDcorresponding to a given waveform is derived by calculation, such as bya processor in the optical inspection tool. RCWA is discussed inChateau, “Algorithm for the rigorous couple-wave analysis of gratingdiffraction”, Journal of the Optical Society of America, Vol. 11, No. 4(April 1994) and Moharam, “Stable implementation of the rigorouscoupled-wave analysis for surface-relief gratings: enhancedtransmittance matrix approach”, Journal of the Optical Society ofAmerica, Vol. 12, No. 3 (May 1995).

The measured CD and profile are used by processor 320 at step 3100 todetermine etch process parameters (i.e., a trim recipe) for wafer W, asby an equation that takes into account the CD and profile anglemeasurements as well as characteristics of etcher 370. Etch processparameters that can be adjusted by processor 320 employing such anequation include etch power, etch time, etch gas flow rate and pressure,magnetic field intensity and magnetic field profile.

To obtain correct final CD and profile, both photoresist trim andunderlying layer etch recipes can be adjusted for each wafer. Forexample, final CD is most affected by the trim recipe, and final profileis most affected by the etch recipe. The relationships between measuredpre-etch CD and profile, trim and etch recipes, and final CD and profileare determined empirically prior to the start of production. A series ofexperiments are conducted by first determining pre-etch CD and profile,then performing trim and etch processes, then mapping the results. Forexample, a series of experiments changing trim time and etch recipe canbe conducted to obtain the best results, and to determine how each ofthe trim and etch recipes affect the final results. The experimentalresults can be expressed in algorithms or equations which the processoruses during production to calculate the trim and etch parameters.

In one embodiment of the present invention, the photoresist trim time isadjusted while the other parameters of the trim recipe, as well as theetch recipe for the underlying layer, are kept constant. In thisembodiment of the present invention, before the integrated OCD/etchprocess can be performed, a “trim curve” for calculating the trim timemust be determined. This involves conducting a design of experiments(DOE) wherein a series of wafers is etched with different trim times,keeping the rest of the trim etch recipe constant. FIG. 4A is an exampleof a trim curve. The amount trimmed (the difference between pre-etch andpost-etch CD) is shown to be a function of both trim time andphotoresist (PR) sidewall angle. The dependence of the amount trimmedvs. PR sidewall angle (SWA) is plotted in FIG. 4B. To avoid thecomplication of within wafer non-uniformity due to etcher and pre-etchnon-uniformity, the data are taken from the same die of the series ofwafers etched under the same conditions. It can be seen in FIG. 4B thatthe amount trimmed increases with the SWA. This behavior is intuitivelycorrect, since a re-entrant profile (SWA>90°) is conducive to CD loss inan etch process.

The trim time determination for a given target post-etch CD isillustrated with the trim curve of FIG. 4A plotted as a function of SWA,as shown in FIG. 4C. The dependence of the trim amount on the trim timeand sidewall angle can be combined into a single mathematical formulafrom the two formulas shown in FIG. 4C. If we assume that all responsesare linear with time, as shown in FIG. 4C, then the change in CD (“ΔCD”)can be expressed in the following equation of a line:

 ΔCD=R(A)t+S(A)  (1)

where t is the trim time and R(A) and S(A) are given by Equations 4 and5 below. If two trim times for which the trim curve has been determinedare referred to as t₁ and t₂, where t₂ is greater than t₁, and thesidewall angle is referred to as A, thenΔCDt ₂ =R(A)t ₂ +S(A)=p ₂ A+q ₂  (2)andΔCDt ₁ =R(A)t ₁ +S(A)=p ₁ A+q ₁  (3)where p and q are constants obtained from a well-known linear best fitanalysis (such constants are shown in the equations in FIG. 4C).

Equations (2) and (3) can be solved for R(A) and S(A) as follows:R(A)=((p ₂ −p ₁)A+q ₂ −q ₁)/(t ₂ −t ₁)  (4)S(A)=((p ₁ t ₂ −p ₂ t ₁)A+q ₁ t ₂ −q ₂ t ₁)/(t ₂ −t ₁)  (5)

Equations (4) and (5) can be substituted into Equation (1) to yield aformula that determines the trim time t necessary to achieve the targetpost-etch CD for a given pre-etch CD and SWA. This formula is used byprocessor 320 in step 3100.

In another embodiment of the present invention, the present methodologyalso takes into account the fact that trim time versus the amount ofphotoresist trimmed is non-linear, as shown in FIG. 4D. Thus, thepresent invention enables more accurate photoresist trimming.

To test the CD control of the methodology of the present invention, aseries of wafers was run with a target final CD of 130±1 nm. The averagepre-etch CD was 162.6 nm with a full range (maximum-minimum) of 8.36 nm.Nine-point measurements were performed on each wafer, and the average CDand PR SWA for each wafer were fed forward to the etcher. The onlychange in the entire process sequence was the trim time, which wascalculated automatically based on the trim curve information stored inthe recipe. FIG. 5A shows the results which indicate that the finalpost-etch CD distribution is significantly reduced from that of thepre-etch distribution. The full range wafer averaged pre-etch CDdecreased from 8.36 nm to a post-etch value of 1.61 nm. The tightcontrol also achieves the final post-etch CD of 130.1 nm, which meetsthe target range of 130±1 nm.

To obtain these results, it is beneficial to have a very stable etcher,because typically the entire system does not operate on closed loopcontrol. In other words, to be able to use the best known method etchand trim recipes keeping them constant, the etch chamber must first becharacterized. For example, the trim curve, shown in FIG. 4A, wasdetermined two days before the wafers used in FIG. 5A were run. Thefinal post-etch CD results indicate excellent etcher stability. Incertain embodiments of the present invention discussed below, final CDand profile results can be fed back to processor 320 to adjust the trimcurve (and hence trim time) due to drift in the etch step. In this way,lack of long-term etch chamber stability can be taken into account.

The present invention provides a unique solution to the gate CD controlproblem that exists today in the semiconductor fabrication industry. Itsolves this problem by measuring both photoresist CD and profile. Theinclusion of the PR profile in the measurement enables, for the firsttime, a 2nd order correction for the contribution of the PR sidewallangle (the “Theta Transformation”). The importance of the ThetaTransformation is shown in FIG. 5B, where the measured post etch CDsobtained with the Theta Transformation are compared with simulated dataobtained with only CD correction and no SWA correction. As shown in FIG.5B, the use of the Theta Transformation tightens the post-etchdistribution from 2.72 nm to 0.62 nm.

Referring again to FIG. 3, at step 3200 photoresist layer 250 is etchedusing the trim recipe (i.e., trim time) determined by processor 320using the experimentally determined equation. The result is shown at theright side of FIG. 2, wherein patterns P are trimmed to dimension CD₁.Underlying layer 210 is then etched, typically at the same etch chamber,in step 3300, resulting in structures S being formed (see bottom rightof FIG. 2). Wafer W is thereafter optionally brought to a photoresistash strip chamber (see step 3400), and brought back to measuring tool310 at step 3500. The CD and profile of structure S are measured atseveral locations on wafer W, such as the locations where the pre-etchmeasurements of photoresist layer 250 were taken at step 3000.

Post-etch CD and profile information is supplied to processor 320, wheredeviations from target results can be used to adjust the trim and/oretch recipe for the next wafer to be etched. For example, from themeasured CD and profile and the previously developed DOE modeling,etcher process drift can be determined; that is, etcher process “age” orwhere the etcher is on its process timeline. The etch recipe can then beadjusted for the next wafer, so the etch results are closer to thetarget. Post-etch information can also be fed back to processor 320 todiscover and correct for problems in previous processes; for example, ifthe photoresist on a batch of wafers was baked at the wrong temperature,its trim rate will be different. Thus, if the first etched wafer ismeasured and this mistake is discovered, the trim time can be adjustedby processor 320 for the rest of the wafers to compensate. Moreover, ifthe measured dimensional variation is outside pre-determined boundaries,or if the processing results change dramatically from one wafer to thenext, an alarm can be generated to indicate the etcher should be takenout of service; e.g., for repairs or maintenance.

Although the foregoing embodiment of the present invention adjusts thephotoresist trim time while keeping the rest of the trim recipe and theunderlying layer etch recipe constant, it should be appreciated that infurther embodiments of the present invention, other trim parameters canbe variable for each wafer, and the underlying etch recipe can bevariable for each wafer. For example, the etch and/or trim recipes canbe adjusted to compensate for dense to isolateral CD bias changes fromone wafer to the next. Such embodiments require an appropriate DOE todevelop the proper equations for use by processor 320 to choose thetrim/etch process parameter values.

It should also be appreciated that the present methodology of adjustingan etch recipe based on measured CD and profile is not limited to thephotoresist trim process. It can also be employed when a photoresisttrim is not performed. Since post-etch profile is dependent onphotoresist profile, the post-etch profile of any etched pattern can befine-tuned based on the measured photoresist profile sidewall angleusing the present methodology.

In further embodiments of the present invention, an apparatus forprocessing a semiconductor wafer is provided wherein a wafer is removedfrom a wafer cassette, and a CD and profile of a pattern on a patternedlayer formed on the wafer is measured using an optical measuring tool. Aprocess, such as an etch process, is then performed on the wafer using aset of process parameter values, such as a trim or etch recipe, selectedbased on the pattern CD and profile measurements. Post-etch processing,such as ash stripping and wet cleaning, are optionally performed by theapparatus, then a CD and profile of a structure formed in the underlyinglayer by the etch process are measured at several locations before thewafer is returned to a cassette. The post-etch measurements are fed backto the etcher to adjust the etch recipe for a subsequent wafer. All ofthe transfer and processing steps performed by the apparatus areperformed in a clean environment, thereby increasing yield by avoidingexposing the wafer to the atmosphere and possible contamination betweensteps.

These embodiments of the present invention provide for pre-etch CD andprofile measurements of every wafer and adjustment of the photoresisttrim/etch recipe for every wafer according to its CD and profilemeasurements to correct for process variations in previously visitedtools, such as deposition uniformity variations at a deposition moduleand/or exposure and focus variations at a photo cell. The presentinvention also provides for etch recipe adjustment for etcher processdrift.

An apparatus for processing a semiconductor wafer according to anembodiment of the present invention will now be described with referenceto FIG. 6A. The apparatus comprises a chamber or “mainframe” 901, suchas the Centura™ processing system, available from Applied Materials ofSanta Clara, Calif., for mounting a plurality of processing chambers,e.g., conventional etch processors 902, such as DSPII™ polysilicon etchchambers available from Applied Materials of Santa Clara, Calif., andone or more transfer chambers 903, also called “load locks”. In oneembodiment of the present invention, four etch processors 902 aremounted to mainframe 901. In one exemplary embodiment, three etchers 902are used for etching, and one is optionally used for post-etch cleaning(i.e., removing photoresist polymers and other residue from wafers afteretching). Mainframe 901 is capable of maintaining a vacuum environmentin its interior. A robot 904 is provided for transferring wafers betweenprocessing chambers 902 and transfer chambers 903.

Transfer chambers 903 are connected to a factory interface 905, alsoknown as a “mini environment”, which maintains a controlled environment.A measurement tool 906, such as an optical measurement tool utilizingscatterometry or reflectometry techniques, is mounted inside factoryinterface 905. An example of a tool that can be used as measurement tool906 is measuring tool 310 described above (see FIG. 1), which caninclude the measurement tool described in U.S. Pat. No. 5,963,329. Aprocessor (i.e., a processor corresponding to processor 320) to provideetcher 902 an etch recipe based on the wafer CD and profile measurementsas described above can be part of etcher 902 or mainframe 901. One ormore robots 907, or a track robot, are also mounted inside factoryinterface 905 for transferring wafers between transfer chambers 903,measurement tool 906 and standard wafer cassettes 908 removably attachedto factory interface 905. Mainframe 901, transfer chambers 903, factoryinterface 905 and robots 904, 907 are all parts of a conventionalprocessing system such as the Applied Materials Centura™, andcommunicate with each other while maintaining a clean, controlledenvironment. Such conventional processing systems further comprise aprocessor, such as a computer (not shown) to electronically control theoperation of the system, including the transfer of wafers from one partof the system to another.

The operation of the apparatus according to this embodiment of thepresent invention will now be described with reference to the flow chartof FIG. 7. After a plurality of wafers are processed at a processingtool, such as a photo cell as described above, to form a photoresistmask on an underlying layer, they are loaded into a cassette 908, andthe cassette is transferred to factory interface 905 at step 1010. Awafer is then unloaded from cassette 908 and transferred to measurementtool 906 by robot 907 (step 1020), and the CD and profile of a patternon the photoresist are measured at step 1030. At step 1040, aphotoresist trim recipe for the wafer is selected based on the CD andprofile measurements, as explained above.

At step 1050, the wafer is transferred from measurement tool 906 toetcher 902 using robot 907 to move the wafer to transfer chamber 903,and using robot 904 to move the wafer to etcher 902. The photoresistlayer is trimmed (step 1060), the wafer is then etched (step 1070),typically in the same etcher 902. Next, in certain embodiments of thepresent invention, the wafer is transferred to a photoresist strippingchamber 902 (step 1080), such as a conventional ash strip chamber, forremoval of the photoresist (step 1090). The wafer is then transferredback to measurement tool 906 for a post-etch CD and profile measurement(steps 1100 and 1110) before being loaded into cassette 908 at step1120. The post-etch CD and profile measurements are sent to processor320, and used to correct the trim curve and/or etch recipe for the nextwafer to be etched, as explained above.

In a further embodiment of the present invention shown in FIG. 6B,factory interface 905 a has a CD measurement tool 906 a mounted to it(instead of inside it as in the embodiment of FIG. 6A). The apparatus ofFIG. 6B operates according to the flow chart of FIG. 7 as describedabove.

In a still further embodiment of the present invention illustrated inFIG. 6C, measurement tool 906 a is mounted on mainframe 901 rather thanfactory interface 905 a. The apparatus of FIG. 6C operates according tothe flow chart of FIG. 7 as described above.

In another embodiment of the present invention illustrated in FIG. 6D,factory interface 905 b has a measurement tool 906A and a conventionalwet clean chamber 909 mounted to it. Wet clean chamber 909 can be asingle wafer cleaning station using ultrasonic transducers. One of thechambers 902 on mainframe 901 is a conventional ash strip chamber, asdiscussed above. After a wafer is etched, it is transferred to ash stripchamber 902 for photoresist removal (steps 1080 and 1090 of FIG. 7),then it is transferred to wet clean chamber 909 and cleaned prior to orafter being transferred to measurement tool 906A in step 1100.

In another embodiment of the present invention illustrated in FIG. 6Eand fully described in U.S. patent application Ser. No. 09/945,454,filed Aug. 31, 2000, mainframe 901 is the Applied Materials' Centura™and factory interface 905C is the Link™, also available from AppliedMaterials. Factory interface 905C has a single robot 907A, a measurementtool 906A as described above, a conventional wet clean chamber 909 asdescribed above, and a conventional ash strip chamber 910 mounted to it.Additionally, two of the ash strip chambers 910 are mounted on mainframe901, along with two conventional etchers 911. Alternatively, fouretchers 911 can be mounted to mainframe 901 instead of ash stripchambers 910. After a wafer is etched, it is transferred to one of theash strip chambers 910 for photoresist removal (steps 1080 and 1090 ofFIG. 7), then it is transferred to wet clean chamber 909 and cleanedprior to or after being transferred to measurement tool 906A in step1100.

The embodiments of the present invention illustrated in FIGS. 6A-Eprovide pre-etch CD, and profile measurement, etching, cleaning, andpost-etch CD measurement entirely under controlled environmentalconditions. By providing etching, cleaning and measurement tools on themainframe and/or factory interface, the wafer can be etched, cleaned andinspected before being returned to a cassette, thereby reducingprocessing time and cost. Moreover, the embodiments of FIGS. 6A-Dprovide feedback and feed forward of measurement data in real time forevery wafer, thereby enabling etch processing to be customized for everywafer to increase yield. Thus, the present invention provides increasesin yield and decreases in production costs vis-à-vis prior art systems,wherein feedback from CD measurements, if any, is on a lot-to-lot basisrather than for every wafer, and wafers must be exposed to theatmosphere between measuring, etching and cleaning steps.

The present invention is applicable to the manufacture of various typesof semiconductor devices, particularly high density semiconductordevices having a design rule of about 0.18 μ and under.

The present invention can be practiced by employing conventionalmaterials, methodology and equipment. Accordingly, the details of suchmaterials, equipment and methodology are not set forth herein in detail.In the previous descriptions, numerous specific details are set forth,such as specific materials, structures, chemicals, processes, etc., inorder to provide a thorough understanding of the present invention.However, it should be recognized that the present invention can bepracticed without resorting to the details specifically set forth. Inother instances, well known processing structures have not beendescribed in detail, in order not to unnecessarily obscure the presentinvention.

In another embodiment of the invention, a duration T (i.e., trim time T)of the trimming process is calculated for each product wafer tocompensate for a plurality of parameters and manufacturing variablesthat are apparent on pre-etched substrates. The trim time is calculatedas a numerical solution, or “N-parameter critical dimension (CD) controlgraph”, of a mathematical equation, wherein N is a number of parametersand manufacturing variables taken into account in calculations of thetrim time T. The parameters of the trim recipe, as well as parameters ofthe process recipe used for etching a material layer beneath thepatterned mask are kept constant during such trimming and etchprocesses.

The numerical solution is based on sets of pre-trim measurements andpost-etch measurements that are performed upon test substrates prior totrimming and etching the product substrates. Based on these sets ofmeasurements, an empirical model N-parameter CD control graph isgenerated which precisely describes how the etch process results for theproduct substrates can be predicted. The measurements performed on thetest and product wafers are generally non-destructive measurements(e.g., optical non-destructive measurements) that are performed for astatistically sufficient number of regions (e.g., 5-9 regions) on awafer and then averaged to compensate for non-uniformity of the measuredparameter within the wafer. Such measurements may generally be performedusing measuring tools which are components of a semiconductor waferprocessing system (discussed in reference to FIGS. 6A-6E above). In analternate embodiment, stand-alone measuring tools may also be used toinspect the wafers.

Advanced process control techniques may be applied to semiconductormanufacturing processes. These techniques may be applied to gate levelcritical dimension (CD) control, although they can be applied to mostsemiconductor manufacturing processes. The primary goal of processcontrol in manufacturing is to maintain the process output to be withinthe lower and upper specification limits (LSL and USL). There is aninput and output for every process tool. For most process tools, theoutputs are correlated to their respective inputs and for all processtools the outputs are effected by the process tool condition.

The controlled parameter of the input and output of each process toolcan be modeled as an average value with a finite noise levelsuperimposed on it. Due to the finite resolution of each process tool,each tool “adds” noise to the input objects. As a result, the noiselevel at the output is expected to be higher than at the input. Thisnoise reduction proposition has been applied to gate-level etch CDcontrol. In such application, the controlled parameter is the gate CDand the noise that is of interest at the output is the wafer to wafer CDrepeatability. By measuring the CD of the incoming wafers andfeed-forwarding this measured quantity to the etcher, the etcher canthen use this information to adjust the etch recipe so that thewafer-to-wafer CD distribution at the output (FIG. 9A graph 840) isbetter than the input (FIG. 9A graph 833). This noise reduction filterbehavior of the feedforward controller 835 is illustrated in FIG. 9A.

In order for this control technique to work, the resolution of thecontroller 835, including its functional blocks, has to be significantlysmaller than the input noise level. The functional blocks of thecontroller 835 are depicted in FIG. 9B. The entire process starts withan automatic measurement performed at the input. The measurement can bedone either by an integrated or stand-alone metrology tool 850. Theresults of this measurement, Q, are fed-forward to a controller 852. Thecontroller 852 has a built-in etch process model that accuratelypredicts the outcome of the etch process tool based on Q. The controller852 produces the necessary process condition P to an etcher 854 (etchtool). The result is that the outputs of the etcher quantified as T witha noise component η which is significantly smaller than that of theinput noise level. Further enhancement in noise reduction is achieved byusing a second metrology tool 859 to measure output parameters and feedthe parameters back along path 860 to the controller 852.

The noise component η is a measure of the resolution of the entiresystem including not only the resolution of the metrology tool 850 andthe process tool (etcher 854) but also the second metrology tool 859used to quantify the results at the output. In principle, thisfeed-forward controller 852 is sufficient to control the output to bewithin the USL and LSL (graphs 533 and 540 shown in FIG. 9A). Furtherenhancement in noise reduction is achieved by using a second metrologytool 859 to measure output parameters and feed the parameters back alongpath to the controller 852.

The N-parameter CD control graph defines the trim time T for eachproduct wafer as a multi-parameter function of a plurality of parametersassociated with the patterned mask to be trimmed and an underlying layerto be etched using the trimmed mask as an etch mask. Generally, suchparameters include an amount of the mask material (e.g., photoresist) tobe removed (i.e., trimmed), a sidewall angle (SWA) of a trimmed elementof the patterned mask, width of a foot of such an element, thickness ofthe patterned mask, thickness of the material layer beneath thepatterned mask, and the like.

The CD control graph can be written mathematically as follows:ΔCD=CD _(pre) −CD _(post) =R(t, Q ₁ , Q ₂ , . . . , Q _(N))  (6a)where R is the response function of the etch tool, t is the trim time,and Q_(i), is the ith pre-etch measured parameter fed forward from themeasurement tool. CD_(post) in this case is the target CD, T. Since t isthe only unknown in Eq. (6a), it can solved by solving Eq. (6a).

In another embodiment, the trim process condition can be a variable. Inthis case the CD control graph takes the following fork:

 ΔCD=CD _(pre) −CD _(post) =R(P, Q ₁ , Q ₂ , . . . , Q _(N))  (6b)

where P is a trim process parameter. P can be one of gas flow rate,pressure, rf power, and the like. In this case P will be the solution ofthe control graph.

The amount of the photoresist to be trimmed is defined herein as adifference between widths of the pre-trimmed element (e.g., line,column, space between the lines or columns, and the like) of thepatterned mask and the post-trim target width of such an element of themask. Correspondingly, the term “sidewall angle” is used in reference tothe angle formed between a sidewall of the pre-trimmed element of thepatterned mask and a surface of the underlying layer, and the term“foot” is used in reference to the form factor of a bottom portion ofthe pre-trimmed element, respectively. The sidewall angle and foot ofthe element of the patterned mask are defined in a cross-sectional viewof the mask. The trimming process is generally an isotropic etch process(e.g., isotropic plasma etch process) that is performed upon a patternedmask to reduce width of the features of such a mask.

The N-parameter CD control graph may compensate for variables associatedwith-the etch process that uses the trimmed mask as the etch mask, aswell as for variables associated with the etch reactor performing suchan etch process.

In one embodiment, a group of the test wafers that are trimmed using thepre-defined N-parameter CD control graph (i.e., each such wafer trimmedfor the calculated trim time T) is then etched in the etch reactor.After the etch process, critical dimensions (e.g., width) of the etchedfeatures are measured and compared with the target values for suchdimensions. Then, the N-parameter CD control graph is modified such thatthe features of the patterned mask on the product wafers are trimmed tothe pre-determined width (i.e., for the modified trim time T) therebyfacilitating, during the etch process, etching the features having thepre-determined (i.e., target) critical dimensions (CDs).

FIGS. 8A-8B depict a flow diagram of a method of calculating the trimtime T or trim process condition in accordance with one embodiment ofthe present invention as a sequence 800. The sequence 800 comprisesprocessing steps that are performed on the test and product substratesduring the trim and post-trim etch processes. In FIGS. 8A-8B, numeralsin parenthesis designate the links that interconnect portions of theflow diagram depicted in FIG. 8A and FIG. 8B, respectively.

The sequence 800 starts at step 801 and proceeds to step 802 when apatterned mask (e.g., photoresist patterned mask) is formed on anunderlying layer or layers that are deposited on a semiconductorsubstrate, such as silicon (Si) wafer, and the like. The underlyinglayer may also comprise a top film of an anti-reflective coating, (ARC).In one application, the underlying layers comprise a gate electrodelayer (e.g., polysilicon layer) and gate dielectric layer of a gatestructure of a field effect transistor (e.g., complementarymetal-oxide-semiconductor (CMOS) field effect transistor, and the like).

In one application discussed herein, the patterned mask is a photoresistpatterned mask, or photoresist mask. The photoresist mask is generallyformed using a photolithographic process. Due to optical limitations ofthe photolithographic process, the photoresist mask generally compriseselements that represent scaled-up replicas of the features to be etchedin the underlying layer or layers. As such, after the photolithographicprocess, the photoresist mask should be trimmed before such a mask maybe used as an etch mask.

In an alternate application, the patterned mask may be formed from othermaterials, e.g., amorphous carbon (i.e., α-carbon), Advanced PatterningFilm™ (APF) available from Applied Materials, Inc. of Santa Clara, andthe like. Such masks are generally fabricated using sacrificialphotoresist masks and, as such, also should be trimmed before used asthe etch masks.

At step 804, pre-trim measurements are performed on test wafers. Thetest wafers generally comprise the patterned mask and underlying layerthat are substantially similar to such of the product wafers. Thepre-trim measurements generally comprise measurements of parametersselected, in a specific application, for an N-parameter CD controlgraph. Depending on the application, different combinations ofparameters of the patterned mask and the underlying layer may beselected for the N-parameter CD control graph based on a degree of theircontribution to yield of the trimming and etch processes.

Generally, the parameters associated with the element (or elements) ofthe patterned mask having smallest width (i.e., elements having criticaldimensions) are selected for use in calculations of the trim time T.Herein such elements of the patterned mask are referred to as criticalelements.

In one exemplary embodiment, the trim time T is calculated as a functionof one parameter, i.e., N=1. Such parameter may be for example, e.g.,pre-trim width and sidewall angle of the critical element of thepatterned mask, thickness of the underlying layer or, alternatively,width of the foot of such a critical element. It is believed that onesuch parameter has most impact on accuracy of calculating the trim timeT in applications, such as etching a gate electrode of a gate structureof a CMOS transistor, and the like.

Thickness of the underlying layer defines a duration of the etchprocess. The etch process has a finite directionality and, as such,material forming the sidewalls of the etched feature, as well thematerial of the etch mask are consumed as the etch process progresses.Therefore, to compensate for such losses during the etch process, theetch process may use an etch mask having an initial width (i.e.,post-trimmed width) that is greater than the target width of the etchedfeature.

In alternate embodiments, a number of parameters of the patterned maskused to calculate the trim time T may be greater than 1. However, insuch an embodiments, the trim time T may be calculated using the samemethodology as in the described below embodiment having N=1.

At step 806, a trim time for the test wafers is selected. The testwafers are trimmed for a specific pre-determined time that is selectedwithin a time interval between the anticipated maximal and minimalduration of the trimming process when such a process is performed on theproduct wafers.

At step 808, the patterned masks of the test wafers are trimmed for thepre-defined time (discussed in reference to step 806 above). Step 808generally uses same trimming recipe that is used to trim the patternedmasks of the product wafers.

At step 818, the test wafers are etched using the trimmed patternedmasks as etch masks. Step 818 generally uses same process recipe that isused to etch the product wafers. The wafers may be trimmed and etchedeither in separate reactors or in the same etch reactor, such as theDecoupled Plasma Source (DPS) II module of CENTURA® semiconductor waferprocessing system available from Applied Materials, Inc. of Santa Clara,Calif. After the etch process, the photoresist mask may be optionallystripped using, for example, the Advanced Strip and Passivation (ASP)module or AXIOM® module of the CENTURA® system.

At step 820, the test wafers undergo the post-etch measurement of thewidth (i.e., critical dimension) of the features etched in theunderlying layer during step 818. In one exemplary embodiment, thepost-etch measurements comprise measurements of the width of thepolysilicon gate electrode of a gate structure of the CMOS transistor.Such post-etch measurements may generally be performed using the samemeasuring tools that are employed for the pre-trim measurements(discussed in reference to step 804 above).

At step 822, the N-parameter CD control graph is defined using theresults of measurements performed during steps 804 and 820. Assumingthat the etch rate during a trimming process does not depend on theabsolute value of a measured parameter, the equation for ΔCD may beexpressed using the following mathematical formula for the 3-parameterCD control graph:ΔCD=C _(PRE) −C _(TARGET) =f+t ₁ T+t ₂ T ² +a ₁ A+a ₂ A ² +x ₁ AT+b ₁B+b ₂ B ² +x ₂ BT+x ₃ AB+x ₄ ABT,  (7)where T is the process time (i.e., trim time) of the trimming process,C_(PRE) is a pre-trim width (the first measured parameter) of a criticalelement of the patterned mask, C_(TARGET) is a target (i.e., post-trim)width of the critical element, ΔCD is a difference between thepre-trimmed width and the target width, A is a second measured parameter(e.g., sidewall angle), B is a third measured parameter (e.g., thicknessof the underlying layer to be etched), and the f, t₁, t₂, a₁, a₂, x₁,x₂, x₃, and x₄ are coefficients of the CD control graph. Thesecoefficients are obtained by building a statistical model that best fitto the measured data.

The equation (7) may be generalized in the following form:n+mT+t ₂ T ²=0  (8)wheren=f+a ₁ A+a ₂ A+b ₁ B+b ₂ B ² +x ₃ AB−C _(PRE) +C _(TARGET)  (9)m=f+x ₁ AT+x ₂ BT+x ₄ ABT.  (10)

The equation (8) may be further solved for the trim time T:T=−n/m,if t ₂=0;  (11)T=((m ²−4t ₂ n)^(1/2) −m)/(2t ₂), if t ₂16 0.  (12)

For the 3-parameter CD control graph, the coefficients in equation (8)are defined by the following expressions:n=f+a ₁ A+a ₂ A+b ₁ B+b ₂ B ² +x ₃ AB−C _(PRE) +C _(TARGET)  (13)m=t ₁ +x ₁ AT+x ₂ B+x ₄ AB.  (14)

For the 2-parameter CD control graph when B=0, the coefficients inequation (7) are defined by the following expressions:n=f+a ₁ A+a ₂ A ² −C _(PRE) +C _(TARGET)  (15)m=t ₁ +x ₁ AT.  (16)

Correspondingly, for the 1-parameter CD control graph when A=B=0, thecoefficients in equation (8) are defined by the expressions:n=f−C_(PRE)+C_(TARGET), m=t₁, and t₂=0.

Calculations solving the equation (8) define the N-parameter CD controlgraph. Such calculations may be performed, e.g., in step 3100 using theprocessor 320 (discussed in reference to FIG. 1 above).

Equation (8) can be generalized to a polynomial of degree m in T, wherem is an integer larger than 2.

The N-parameter CD control graph may be re-calculated (or modified) tocompensate for other manufacturing variables using corrective iterationsbased on results of additional pre-determined tests and measurements.For example, to compensate for non-linearity of the trimming process,the test wafers may be measured based on the thickness of thephotoresist mask. The results derived from trimming such wafers may beincluded, as a corrective factor (i.e., feedback), in calculations ofthe process time T using equations (7) through (16).

FIG. 10 depicts an illustrative example of a 2-parameter CD controlgraph where the trim time T is plotted as a function of the ΔCD andsidewall angle. An illustrative example of a 1-parameter CD controlgraph is depicted in FIGS. 4A and 4B, where the trim time T is plottedas a function of the ΔCD (FIG. 4A) and sidewall angle (FIG. 4B).

Each point on the N-parameter CD control graph represents a solution forthe trim time T related to a given set of the measured (i.e., C_(PRE),A, and B) and target (C_(TARGET)) parameters of the patterned mask. Theprocessor of the semiconductor wafer processing system can transformsuch information into the setting for a specific process time (i.e.,specific trim time T) for trimming the patterned mask (e.g., photoresistmasks) of each one of production wafers.

In further embodiments, a number of parameters that define theN-parameter CD control graph may further be increased to compensate forother manufacturing variables, such as the width of the foot of acritical element of the patterned mask, hardness of the photoresistmask, and the like. Accuracy of calculating the trim time T generallyincreases along with the number of the parameters (i.e., manufacturingvariables) that are used in calculations of the trim time.

At step 824, the pilot product wafers are measured. Thereafter, at step828, a pilot batch of the product wafers are trimmed using a timeinterval based on the N-parameter CD control graph. At step 830, thewafers are measured to determine whether the CDs of features areachieved. If the query is negative, the CD control graph is updated andthe method proceeds to step 828 and another batch of pilot wafers areprocessed using a different time interval based on the updatedN-parameter CD control graph. If the query of step 830 is affirmativelyanswered, the method proceeds to step 832.

At step 832, the sequence 800 ends.

In one exemplary application, the disclosed method of calculating thetrim time T and the N-parameter CD control graph was used duringfabrication of a polysilicon gate electrode of the gate structure of aCMOS transistor. In this application, the target width (i.e., CD) of theelement of the patterned photoresist mask was of about 180 nm and the 3σdistribution for such a CD was about 10 nm. With the technologydescribed herein, the post etch distribution of these wafers weretightened to 3.3 nm 3σ with a one parameter (pre-etch CD) CD controlgraph and 1.8 nm 3σ with a two parameter (pre-etch CD and pre-etchPhotomask sidewall angle) CD control graph.

Using the sequence 800A of the present invention, the target range(i.e., post-etched range) of the CDs of the elements of the productwafers was reduced. Specifically, use of the 1-parameter (CD_(PRE)) trimsurface reduced the range of such distribution to about 3-4 nm 3σ whilefurther use of the 2-parameter (CD_(PRE) and sidewall angle) trimsurface further reduced the range to about 2 nm 3σ.

Similar to the embodiment discussed above, the calculated trim time maybe further modified to compensate for other manufacturing variablesusing one or more corrective iterations, as well as the number ofparameters defining the N-parameter CD control graph may be greater thanthree.

The discussed embodiments of the inventive method provide tightstatistical distribution of the critical dimensions of the trimmedpatterned masks and facilitate high dimensional accuracy of the featuresetched in the underlying layers when such trimmed masks are used as theetch masks.

The invention may be practiced using other semiconductor waferprocessing systems and measuring tools wherein the processing parametersmay be adjusted to achieve acceptable characteristics by those skilledin the arts by utilizing the teachings disclosed herein withoutdeparting from the spirit of the invention.

Although the forgoing discussion referred to trimming the patternedmasks used during etch processes, other processes used for fabricatingthe integrated circuits can benefit from the invention.

1. A method of controlling etch processes during fabrication ofsemiconductor devices in a semiconductor substrate processing system,comprising: (a) defining an N-parameter critical dimension (CD) controlgraph to calculate a trim condition for trimming features on thesubstrate to a pre-determined width; (b) providing the substrate havinga patterned mask; (c) trimming the patterned mask for a time calculatedusing the N-parameter critical dimension (CD) control graph; and (d)etching an underlying layer on the substrate using the trimmed patternedmask as an etch mask.
 2. The method of claim 1 wherein step (a)comprises: (a1) providing a plurality of test substrates, each testsubstrate having a patterned mask; (a2) measuring parameters of afeature of the mask; (a3) trimming features of the mask using an etchprocess; and (a4) measuring parameters of the trimmed feature on each ofsaid substrates.
 3. The method of claim 2 wherein the step (a2) isperformed using a non-destructive optical measuring tool having at leastone measuring instrument.
 4. The method of claim 2 wherein the steps(a2) and (a4) further comprise: performing a plurality of measurementson the test substrate; and averaging results of the measurements.
 5. Themethod of claim 2 wherein the measuring parameters are selected from agroup consisting of a width of the feature, a sidewall angle width ofthe feature, a width of a foot of the feature, a thickness of said mask,non-linearity of an etch rate during trimming the feature, and athickness of the layer beneath the mask.
 6. The method of claim 2wherein the step (a4) comprises measuring the width of the feature. 7.The method of claim 2 further comprises: (a5) defining a trim time as asolution of a mathematical equation that uses results of measurementsperformed during the steps (a2) and (a4).
 8. The method of claim 7further comprises: (a6) modifying said trim time using iterations basedon measurements performed using product substrates.
 9. The method ofclaim 2 wherein the steps (a2) through (a4) are performed usingprocessing, metrological, and data computing modules of saidsemiconductor substrate processing system.
 10. An apparatus forcontrolling etch processes during fabrication of semiconductor devicesin a semiconductor substrate processing system, comprising: (a) ameasuring tool for measuring a profile of a feature of a patterned maskand a feature etched in a layer beneath said mask; (b) a processorcalculating an N-parameter CD control graph defining a trim time fortrimming the feature to a pre-determined width; (c) an etch reactorperforming trimming of said mask; and (d) an etch reactor performingetching of said layer using the trimmed patterned mask as an etch mask.11. The apparatus of claim 10 wherein the measuring tool is anon-destructive optical measuring tool having at least one measuringinstrument.
 12. The apparatus of claim 10 wherein the measuring toolmeasures parameters selected from a group consisting of a width of thefeature, a sidewall angle width of the feature, a width of a foot of thefeature, a thickness of said mask, non-linearity of an etch rate duringtrimming the feature, and a thickness of the layer beneath the mask. 13.The apparatus of claim 10 wherein the processor defines the trim time asa solution of a mathematical equation that uses the results ofmeasurements performed by the measuring tool.
 14. The apparatus of claim10 wherein the processor modifies the trim time using iterations basedon measurements performed using product substrates.
 15. The apparatus ofclaim 10 wherein the processor modifies said trim time using a methodcomprising: measuring dimensions of a feature etched in the underlyinglayer of a test substrate; and modifying the trim time for trimming apatterned mask of a product substrate based on the results of measuringsaid dimensions.
 16. The apparatus of claim 10 wherein processes oftrimming the patterned mask and etching the layer beneath said mask areperformed in one etch reactor.
 17. The apparatus of claim 10 furthercomprising a reactor for stripping the patterned mask.
 18. The apparatusof claim 10 further comprising at least one substrate robot fortransferring substrates within the apparatus.